(1) Field of the Invention
The present invention relates to a process for producing ceramic structural bodies by extrusion.
(2) Related Art
In general, it is a conventional practice that a ceramic body is obtained by mixing a solvent, a shaping aid such as a binder and a surface active agent at need with a ceramic raw material and kneading the mixture, and ceramic structural bodies are produced by extruding the ceramic body by using a ceramic structural body-extruding die. The ceramic structural body-extruding die has a structure provided with discharge channels in the form of a slot-shaped lattice and feed passages for dividingly feeding the ceramic body to intersections of the slots of the lattice.
As the shaping aid to be used for the formation of the ceramic body, an appropriate one has been selected heretofore, depending upon uses, among organic binders such as methyl cellulose, carboxymethyl cellulose and polyvinyl alcohol, surface active agents and wax, as disclosed in unexamined Japanese patent application Laid-open No. 2-255,576.
When the ceramic body is extruded through the above-mentioned die provided with the discharge channels in the form of the slot-shaped lattice and the feed passages for dividingly feeding the ceramic body to intersections of the slots of the lattice, the following defects occur. That is, when the above conventional ceramic body is used, an outer peripheral surface of the extrudate becomes rough due to frictional resistance between the ceramic body and the wall surfaces of the metal die. Consequently, a surface portion of the extrudate is stripped or cracked. Further, ribs (walls) constituting the lattice are waved in an extruding direction. Furthermore, the ribs are extruded, but not united to form the lattice.
It is known that the above phenomenon becomes more conspicuous, as the hardness of the ceramic body increases and/or as the fluidity (plastic deformation) drops. However, if hardness of the ceramic body is merely lessened to enhance the fluidity, there occurs the problems in that the extruded ceramic structural body is deformed due to its self-weight or the extrudate is easily deformed with external forces such as vibration generated in the succeeding step.
On the other hand, as mentioned above, it is formerly known that solid wax is incorporated into the ceramic body. However, wax is not dissolved into water, and difficult to be uniformly dispersed into the ceramic body. Accordingly, uniform ceramic body cannot be obtained, and no sufficient effect can be obtained.